1. Field of the Invention
The present invention relates to a method for reducing piston deposits in an internal combustion engine by using a soluble ashless detergent and a heterogenous strong base immobilized within the lubricating system of the engine.
2. Discussion of Related Art
The optimum functioning of an internal combustion engine (especially a diesel engine) requires that fuel combustion acids (e.g., carboxylic, nitric, nitrous, sulfuric and sulfurous acids --with or without alkyl groups) be neutralized where they first contact the lubricant, i.e., at the piston. In the absence of this acid neutralization, the lubricant gels, its viscosity rapidly increases, and engine deposits are formed. This results in increased oil consumption and engine wear.
Traditionally metal-containing (i.e. ash-containing) detergents (e.g., barium, calcium, or magnesium overbased sulfonates or phenates) have been used to neutralize combustion acids (See, for example, U.S. Pat. Nos. 2,316,080; 2,617,049; 2,647,889; and 2,835,688). In the absence of metal detergents, as for example in ashless oils, polyethyleneamine based dispersants have been used for neutralization (See, for example, U.S. Pat. No. 3,172,892, the disclosure of which is incorporated herein by reference). However, ashless detergents are generally not used in lubricating oils because polyethyleneamines are less cost effective than ash-containing detergents and normally do not maintain adequate TBN (Total Base Number).
Well formulated lubricants containing metal detergents are very effective in reducing piston deposits. Often, however, a limit is reached where it becomes increasingly more difficult to further reduce piston deposits. As this limit is approached, an appreciable percentage of piston deposits results from the metal component of the detergents. For example, the deposits on some pistons contain up to 34 wt.% calcium and magnesium. (See A. Sohetelich et al., "The Control of Piston Crown Land Deposits in Diesel Engines Through Oil Formulation," Soc. Automat. Eng. Tech., Pub. Ser. 861517 (1986)). Therefore, it would be desirable to have available a simple and convenient, yet cost effective, method for reducing piston deposits in an internal combustion engine and, preferably, for transferring or moving the deposits to a part of the engine's lubrication system where they will not impair engine performance.